Age-related deficits in perception and memory have frequently been attributed to decrements in the amount of attention available for performing a particular task (i.e., attentional capacity). The empirical data that are available, however, do not necessarily lead to the conclusion that an age-related reduction in attentional capacity exists. The experiments described in the present proposal are designed to provide a more direct and accurate measurement of age differences in attentional capacity than is currently available. All of the experiments employ a concurrent-task methodology, in which subjects perform a choice reaction-time task with visual stimuli (the primary task) and a simple reaction-time task with auditory stimuli (the secondary task) simultaneously. Previous research with young adults indicates that as the amount of attention demanded by the primary task increases, perfgormance of the secondary task is correspondingly impaired. Changes in secondary-task reaction time can thus serve as an index of the attentional capacity allocated to the primary task. The proposed project will examine age differences in the amount of attention available for performing visual search as the primary task. Each trial of the primary task requires subjects to decide whether a particular target letter is present in a visual display. The attentional demands of several aspects of visual search will be investigated: The first two experiments will compare the visual encoding and memory comparison requirements of the task. Experiments 3 and 4 will focus on subjects' ability to use advance information regarding target location and to ignore irrelevant items in the display. Experiments 5 and 6 will investigate the influence of semantic relationships on search performance. Throughout the project, the amount of attention required by a task will be empirically distinguished from the duration of attention within a task. The results of the experiments are intended to improve current theories of age-related changes in cognition and to suggest whether attention is a potentially important variable in the development of rehabilitative procedures.